Primary renal carcinoid tumor

Case contributed by Dr Michael P Hartung


Left flank pain.

Patient Data

Age: 30
Gender: Female

Very large mass along the anterior aspect of the left kidney measuring 9.3 x 7.6 x 8.3 cm (AP x TR x CC). It appears to be arising from the medial anterior cortex, with loss of distinct tissue plane (best seen on the sagittal reformats). Mild hydronephrosis of the left kidney which is likely due to mass effect, as the left ureter is compressed as it courses around the mass.

Lower attenuation projection medially from the mass measuring 1.6 x 1.4 cm (series S6 image #70). The mass has a mildly thickened and enhancing wall. Internally, there is heterogeneous areas of higher and lower attenuation. There is an attenuation difference on pre and postcontrast imaging of approximately 15-20 Hounsfield units in several locations, suggesting possible but equivocal enhancement. Mildly prominent adjacent periaortic lymph node, indeterminate. 


Ultrasound was performed to see if it is a solid neoplasm or complex cyst. First image shows no doppler flow. Upon review of this image, the tech was instructed to perform careful doppler and spectral interrogation of the mass, and turn down the color velocity scale (hard to see, but it is set at 27 cm/s in first image, and 18 cm/s after). As a result, both color doppler and arterial flow was identified in the mass, indicating a solid renal neoplasm. 

Case Discussion


Kidney/retroperitoneum, mass, left, core biopsy: Renal carcinoid tumor (neuroendocrine tumor)

Primary renal carcinoid tumor is extremely rare, with less than 100 cases reported in literature. Neuroendocrine cells are not a normal part of the kidney. It is hypothesized that small rests of the cells may be acquired through metaplasia, a result of congenital abnormality, abnormal embryonal cellular migration, or represent metastasis of unknown primary. Most are found incidentally or a result of mass effect rather than carcinoid syndrome. Often, the tumors are hypodense and do not enhance.

In this case, there is equivocal but suspected enhancement on the CT, although given the size and appearance, a high suspicion for neoplasm is present. Rather than perform an expensive subtraction MRI, ultrasound was utilized to confirm the vascular nature of this neoplasm.

The ultrasound images are very helpful in demonstrating the important principal of careful Doppler interrogation, as the sonologist originally reported that no flow is present within the mass. However, after encouragement to perform a more careful evaluation, several areas of color Doppler and spectral arterial flow were identified in the solid portion of the mass, indicating that this is not a complex renal cyst compared by hemorrhage but rather a solid, vascular neoplasm. At that point, the patient could proceed directly to image guided biopsy for final pathologic diagnosis.

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